Production of alkoxy-hydroxy-benzaldehydes



Patented May 7, 1940 UNITED STATES PRODUCTION OF ALKOXY-HYDROXY BENZALDEHYDES Ewart Mather and William Edward Hamel,

Wrexham, Wales, assignors to Monsanto .Chemicals Limited, London, England, a British company a No Drawing. Application March 2, 1936, Serial No.'66 ,698. In Great Britain March 4,1935 v 10 Claims.

This invention consists in improvements in or relating to the production of vanillin and like alkoxy-hydroxy-benzaldehydes.

It has already been proposed to produce vanillin (3-methoxy-4-hydroxy-benzaldehyde) by the hydrolysis and oxidation, for example by means of cupric acetate, of trichloromethylguaiacylcarbinol. It has also been proposed to produce 3-ethoxy-4-hydroxy-benzaldehyde (which is commonly known as ethylvanillin but which is referred to hereinafter by the trade-marked name Ethavan) by subjecting trichloromethylguaethylcarbinol in one and the same solution simultaneously or in succession to hydrolysis and oxidation by means of a reducible heavy metal compound. Other suggestions for the same or similar processes include the use of salts of alkaline reaction, containing a non-volatile anion, as condensing agents, and in other cases the use of air, or oxygen, or of nitro-aryl sulphonic or carboxylic acids as oxidizing agents. In such processes it is thought that the trichlorocarbinol compound (produced for example by the condensation of chloral or choral hydrate with a 2-alkoxy phenol) is hydrolyzed to the corresponding hydroxy acid which is then converted to the corresponding benzaldehyde by oxidation, carbon dioxide being eliminated. 7

As an alternative process it has been proposed to condense pyrocatecholmonoalkylether with .glyoxylic acid, and to oxidize the condensation product with compounds of heavy metals or with aromatic nitro bodies; no specific example of the aromatic nitro bodies to be employed has, however, been given.

It is an object of the present invention to provide a process whereby vanillin and like al-. koxy-hydroxy-benzaldehydes may be obtained in good yieldson a large scale.

According to the present invention a process for the production of vanillin and like alkoxyhydroxy-benzaldehydes comprises oxidizing a compound having the general formula:

I CHLOE COOH nitrobenzene and their homologues.

heating (for example at temperatures above C. and below 170 C.) in an aqueous solution of caustic alkali with an aryl nitro compound in which the aryl group does not contain any negative substituent. I

The present invention is not restricted to any particular method for the preparation of [the hy-. droxy acid, but preferably in carrying outthe present invention the hydroxy acid is obtained by hydrolyzing the trichlorcarbinol compound produced by the condensation of chloral or chloral hydrate with a 2-alkoxy phenol. The hydrolysis by the aqueous alkali and the oxidation of the hydroxy acid (and of related compounds which may possibly be formed at the same time) may be effected either successively or simultaneously. The preferred aryl nitro compound for use in accordance with the present invention is nitrobenzene which is readily availableat a relatively low price. Other compounds which may be employed are, for example, nitrotoluene,.di-

Although fairly good yields are obtained with nitrobenzene on heating at temperatures of 110 C it is found that a temperature of about'150 C; is most convenient when speed of operation is considered as wellas yield ofproduct. In carrying out the invention in order to obtain the necessary temperatures, in mostcases, it will be necessary to efie'ct the' oxidation in an autoclave. During the 7 course of the reaction it-is found that themono- Example I 54.3 grms. of trichloromethylguaiacyl carbinol were dissolved in a solution of '75 grms. of commercial caustic soda of-97 to 98% sodium hydroxide content in 660 ml. water, and25 grms. of nitrobenzene were added. This charge was then heated for two hours at C. in a steel autoclave. After cooling, nitrobenzene and its reduction products were removed by extracting the oxidized charge with benzene. The extracted alkaline solution, was then acidified with hydrochloric acid and the crude vanillin was extracted with ether, when, after removal of this solvent, 31.37 grms. of crude vanillin were obtained. On vacuum distillation, this crude vanillin gave point 72-77 C., i. e., a yield of pure vanillin equal to about of that theoretically obtainable from the carbinol,

Example II 54.3 grms. of trichloromethylguaiacyl carbinol were dissolved in a solution of grms. of commercial caustic potash of 87 to 88%. potassium hydroxide content in 660 ml. of water, and 25 grms. of nitrobenzene were added. This charge J solvent, 30.98 grms. of crude vanillin were ob-. tained. On vacuum distillationthis'gave 85.4%

of its weight of distilled vanillin of melting point 73-78 C., i. e., a yield of pure vanillin equal to about 80% of that theoretically obtainable from the carbinol.

Example III 54.3 grms. of trichloromethylguaiacyl carbinol were dissolved in a solution of 75 grms. of commercial caustic soda of 97 to 98% sodium hydroxide content in 660 ml. water, and 20 grms. of meta-dinitrobenzene were added. This charge was then heated for 2 hours at C. in a steel autoclave. After cooling meta-dinitrobenzene and its reduction products were removed by extracting the oxidized charge with ether. The extracted alkaline solution was then acidified with hydrochloric acid and the crude vanillin was extracted with ether, when, after removal of this solvent, 30.64 grms. of crude vanillin were obtained. On vacuum distillation, this crude vanillin gave 89.7% of its weight of distilled vanillin of melting point 73.5-78 C., i. e., a yieldof pure vanillin equal to about 80% of that theoretically obtainable from the carbinol.

When a copper lined autoclave was used instead of the steel autoclave, a very similar yield of vanillin was obtained.

Example IV 57.1 grms. of trichloromethylguaethyl carbinol were dissolved in a solution of 75 grms. of commercial caustic soda of 97 to 98% sodium hydroxide content in 660 ml. of water and 25 grms. of. nitrobenzene were added. This charge was thenheated for 8 hours at 110 C. in a steel autoclave. After cooling, nitrobenzene and its reduction products were removed by extraction with'benzene. The extracted alkaline solution was acidified with hydrochloric acid and the crude Ethavan (3-ethoxy-4-hydroxybenzaldehyde) extracted with ether. The ether solution was washed with sodium bicarbonate solution, dried over sodium sulphate, and the solvent remo'vedby distillation. 14.75 grms. of Ethavan of melting point 67.5-71.0 C. were obtained, i. e., a yield of pure Ethavan equal to about 40% of that theoretically obtainable from the carbinol.

Example V 57.1 grms. of trichloromethylguaethyl carbinol were dissolved in a solution of 75 grms. of commercial caustic soda of 97 to 98% sodium hydroxide content in 660 ml. of water, and 25 grms. of nitrobenzene wereadded. This charge was then heated for two hours at 150 C. in a steel autoclave. After cooling, nitrobenzene and its reduction products were removed by extraction with benzene.'- The extracted alkaline solution After cooling, nitrobenzene and its was acidified with hydrochloric acid and the crude Ethavan (3-ethoxy-4-hydroxybenzalde hyde) extracted with ether. The ether solution was washed with sodium bicarbonate solution, dried over sodium sulphate, and the solvent, removed by distillation. 28.15 grms. of Ethavan of melting point 66.0-71.5 C. were obtained, 1. e., a yield of pure Ethavan equal to about 80% of that theoretically obtainable from the carbinol.

Example VI 57 .1 grms. of trichloromethylguaethyl carbinol were dissolved in'a solution of 75 grms. of commercial caustic soda of 97 to 98% sodium hydroxide content in 660 ml. of water, and 25 grms. of nitrobenze'newere added. This charge was then heated for 1 hour at C. in a steel autoclave. Aitercooling, nitrobenzene and its reduction products were removed by extraction with benzene. The extracted alkaline solution was acidified with hydrochloric acid, and the crude, Ethavan (3-ethoxy-4-hydroxybenzaldehyde) extracted with ether. The ether solution was washed with sodium bicarbonate solution, dried over sodium sulphate, and the solvent removed by distillation. 30.62 grms. of Ethavan with the rather low melting point of 60-69 C. were obtained.

Example VII 57.1 grms. of trichloromethylguaethyl carbinol were dissolved in a solution of 75 grms. of commercial caustic soda of 97 to 98% sodium hydroxide content in 660 ml. of water, and 25 grms. of commercial meta-nitrotoluene were added. This charge was then heated for 2 hours at 150 C. in a steel autoclave. After cooling, nitrotoluene and its reduction products were removed by extraction with benzene. The extracted alkaline solution was acidified with hy drochloric acid, and the crude Ethavan (3- ethoxy-4-hydroxybenzaldehyde) extracted with ether. The ether solution was washed with sodium bicarbonate solution, dried over sodium sulphate, and the solvent removed by distillation. 27.05 grmsof Ethavan of melting point 68.571.0 C. were obtained, i. e., a yield of pure Ethavan equal to about 80% of that theoretically obtainable from the carbinol.

Example VIII 150 grms. of trichloromethylguaethyl carbinol were dissolved in a solution of 150 grms. of commercial caustic soda of 97 to 98% purity in 1000 ml. of water. The mixture was cautiously heated to boiling and then boiled for 15 mins. at atmospheric pressure, cooled to room temperature, and acidified with 400 ml. of approximately lO-N hydrochloric acid. A sticky resin which formed was filtered ofi and discarded, and the aqueous filtrate extracted with ether. The ether extract was then shaken with a solution of 50 grms. of sodium bicarbonate in 500 ml. water. The ether layer was discarded and the bicarbonate extract treated with 15 ml. of approximately 10-N hydrochloric acid, and then extracted successively with two portions of ether of 250 ml. each, and then with a further 100 ml. portion. The ether extract was evaporated down, and left a small amount of resinous material, which was discarded. The bicarbonate extract was then treated with an excess of hydrochloric acid and extracted with two successive portions of 250 ml. each of ether. This ether extract yielded, on evaporation, 40.4 grms. of crude guaethyl glycollic acid. This solid was purified by recrystallisation from ethylene dichloride, and it then melted at about 126 C. and had an equivalent, determined by titration, of about 213.

zene, and the alkaline aqueous layer acidified with hydrochloric acid and extracted with ether. On evaporation,- the ether solution yielded 21.15 grms. of crude 3-ethoxy-4-hydroxy-benzaldehyde. This crude product, on vacuum distillation, yielded 91.75% of its weight of 3-ethoxy-4- hydroxybenzaldehyde 'of melting point 69-71 C.,

i. e., a yield of the pure product equivalent to about of that theoretically obtainable'from the glycollic acid used.

We claim:

1. A process for the production of alkoxy-hydroxy-benzaldehydes comprising heating a compound having the general formula:

( JHbH in which R. is an allcyl group and X is a group selected from the class consisting of trichloromethyl (CC13) and carboxyl (-COOH) groups, in an aqueous solution of caustic alkali with an aryl nitro compound that is free of .any negative substituent.

2. A process for the production of alkoxy-hydroxy-benzaldehydes comprising simultaneously hydrolyzing and oxidizing a 4-hydroxy phenyl-3- alkoxy trichlorocarbinol compound to the corresponding 4-hydroxy-3 alkoxy benzaldehyde by heating in an aqueous solution of caustic alkali with an aryl nitro compound that is free of any negative substituent.

3. The process of claim 1 wherein, the heating is conducted at a temperature between and compound selected from the group consisting of chloral and chloral hydrate with a 2-alkoxy phenol and hydrolyzing and oxidizing the trichlo'rocarbinolcompound produced to form the corresponding 3-alkoxy-4-hydroxy benzaldehyde, the oxidation being effected by heating in an aqueous solution of caustic alkali with an aryl nitro compound in which the aryl group is free of any negative substituent. I

8. A process for the production of 3-methoxyl-hydroxy-benzaldehyde comprising hydrolyzing trichloromethylguaiacyl carbinol and. then oxidizing the hydrolysis product by heating at a temperature between 110 and C. in an aqueous solution of caustic alkali with an aryl nitro compound selected from the group consisting of nitrobenzene, meta-dinitrobenzene and meta-nitrotoluene.

9. The process of claim 8 wherein the hydrolysis and oxidation are carried out simultaneously. 10. A process for the production of B-ethoxyi-hydroxy-benzaldehyde comprising hydrolyzing trichloromethylguaethyl carbinol and. then oxidizing the hydrolysis product'by heating at a temperature between 110 and 170 C. in an aqueous solution of caustic alkali with an aryl nitro compound selected from the group consisting of nitrobenzene, meta-dinitrobenzene and meta-nitrotoluene.

I EWART MATI-IER.

WILLIAM EDWARD HAMER. 

